Transcript Rocks Get Stressed

Rocks Get Stressed
• Stress is the amount of force per unit area
that is put on a given material.
• When rock changes its shape due to stress,
this reaction is called deformation.
• Rocks can deform due to the force of plate
tectonics.
• Compression is stress caused from
squeezing.
Rocks Get Stressed (cont)
• The Rocky Mountains and the Cascade
Range are two examples of compression at
a convergent plate boundary.
• Tension is stress that occurs when forces act
to stretch an object.
Folds
• Folding occurs when rock layers bend due
to stress in the crust.
• Two most common
– Anticlines – Sinclines
– Another type is a monocline. In a monocline,
rock layers are folded so that both ends of the
fold are still horizontal.
Faulting
• Fault - The surface along which rocks break
and slide past each other.
• Blocks of crust on each side of the fault are
called fault blocks.
• Two sides
– hanging wall
– foot walls
Faulting (cont)
• Normal Fault - causes the hanging wall to
move down relative to the footwall. This
occurs when tectonic forces cause tension
that pulls rocks apart.
• Reverse Fault - causes the hanging wall to
move up relative to the footwall. This
occurs when tectonic forces cause
compression that pushes rocks together.
Faulting (cont)
• Strike slip fault - occurs when opposing
forces cause rock to break and move
horizontally.
Mountain Building
• Three most common types of mountains
– Folded mountains form when rock layers are
squeezed together and pushed upward.
– Fault-block mountains form when faulting
causes large blocks of the crust to drop down
relative to other blocks.
– Volcanic mountains form when molten rock
erupts onto the surface. They form from new
material being added to the crust. Ex: Ring of
Fire.